How can I subdivide and curve/smooth a low poly line without moving the original points
not sure if it is the solution but if you quick add faces to your loop and then use the knife project fonction with the side curve and remove the vertices you don't use in the end.

Draw the side section with curve as you did for the front section.

Then convert all those new curve to meshes with command + c
Join those meshes with command + j

select the new mesh (the one made of the joined one) and then what you have already done for the front of the boat.

use the side view and go to edit mode en press space to search "knife project 

this will cut your mesh where it intersect with the second one